High temperature microhardness of soda-lime glass

The effects of high temperature Vickers indentation of commercial soda-lime glass were investigated. The tests were performed from room temperature up to 400 °C for loads from 5 N to 40 N. The hardness decreased as the temperature was increased. Indentations cracks and crack morphology were investigated by optical and scanning electron microscopy. The radial cracks increased in length with increasing temperature, being in part determined by the E/H dependence on temperature. At room temperature, the load P is proportional to the radial crack length c3/2. As the temperature increases, it is observed that the c exponent decreases. The crack morphology is modified as the E/H ratio varies with temperature. The indentation stress field according to the models of Yoffe and Cook and Pharr indicates that increasing temperature encourages radial crack growth and disfavors median crack propagation.